1. Field of the Invention
The present invention relates to an electrostatic latent image developing toner which is used in developing a latent image formed by electrophotography, electrostatic recording method, or the like, with a developer, a manufacturing method for an electrostatic latent image developing toner, an electrostatic latent image developing developer and an image forming method.
2. Description of the Related Art
In electrophotography, an electrostatic latent image is formed on a photoreceptor by a charging process and an exposure process, and the electrostatic latent image is developed with a developer comprising an electrostatic latent image developing toner (which hereafter may be simply called a “toner”), and visualized through a transfer process and a fixing process. The developer is available as a two-component developer which consists of a toner and a carrier, or as a one-component developer which uses either a magnetic toner or a non-magnetic toner alone. For manufacturing the toner, a so-called kneading and pulverizing method is generally used in which a thermoplastic resin is fused and kneaded together with a pigment, a charge control agent, and a release agent such as a wax or the like, then cooled, pulverized, and further classified.
In recent years, it has been demanded that the image formed by an image forming apparatus using electrophotography has a higher quality, the process have a higher speed, and from the viewpoint of environmental consideration, the production process consume less energy. To meet the demand for higher-quality image, how to make the toner particle size smaller has been investigated; to satisfy the demand for higher-speed process, the low-temperature fixability has been researched; and to accommodate the demand for low energy consumption, improvement of the production method has been vigorously studied.
However, with respect to the conventional toner obtained by the kneading and pulverizing method as mentioned above, there is a limitation in controlling the particle diameter of the toner, and it has been practically difficult to manufacture a toner having a volume-average particle diameter of 6 μm or smaller with a good yield and a narrow particle size distribution. Further, it has been difficult to avoid the disadvantages that, when a toner having a small particle diameter is charged, the variation in charge is great; that fogging is generated on an image formed by the image forming apparatus; that, when image formation is carried out, the toner is scattered, resulting in the inside of the image forming apparatus being fouled with the toner; and the like.
Against these problems, as means for allowing the toner particle diameter and the particle size distribution to be intentionally controlled, methods for manufacturing the toner for electrophotography based on the wet type manufacturing methods, such as the suspension granulation method, the suspension polymerization method, the emulsification polymerization aggregation method, and the like, have been proposed in recent years.
By chemically manufacturing toner particles with these methods, it has become possible to supply a toner with a volume-average particle diameter of 6 μm or less to the market at low cost, which has been actually impossible with the conventional kneading and pulverizing manufacturing method. In addition, when using the conventional kneading and pulverizing manufacturing method, the particle size distribution of the small-diameter toner is broad, and the number of toner particles required per unit area is increased, whereby the charging control of the toner has been difficult, but the wet type manufacturing method has allowed the particle size distribution to be made uniform and the charging control to be facilitated. In such a situation, the demand for higher image quality on the basis of the small particle diameter toner manufactured by the wet type method has been more and more increased.
However, when, in these wet type manufacturing methods, a magnetic toner comprising a magnetic powder to be used for a magnetic 1-component developer or a magnetic 1.5-component developer is manufactured, an excellent particle diameter controllability is provided, but the difference in specific gravity between the magnetic power and the resin particle causes the nonuniform mixing, resulting in a variation in the content of magnetic powder from one toner particle to another, and resulting in a magnetic powder exposed on the toner surface, which have caused problems such that the charge quantity distribution is broadened, and apparatus internal contamination and paper fogging take place.
Then, a prescription of the solubility of the magnetic powder into nitric acid aqueous solution, and a treatment by use of a dispersing agent have been proposed (as disclosed in, for example, Japanese Patent Application Laid-Open No. 2004-287153).
However, when, in the development method using a magnetic toner, the transportability of the toner on the magnet roll in the development apparatus is improved, or the coloring of the toner is improved in order to reduce the amount of the toner consumption, it is necessary to increase the addition amount of the magnetic powder. At this time, if the addition amount of the magnetic powder is over 50% by mass, the dispersion of the magnetic powder in the toner is insufficient, which has caused problems such that a reduction in toner charge quantity or a degradation of the charge quantity distribution is occurred, and an apparatus internal contamination and paper fogging take place.
Especially, in the emulsification polymerization aggregation method, it is necessary that the dispersion liquid be uniformly stirred at the time of the aggregation for the uniform aggregation, however, the difference in specific gravity between the magnetic power and the resin particle prevents uniform mixing, resulting in a variation in the addition amount of magnetic powder from one toner particle to another, and resulting in exposure of the magnetic powder on the toner surface being increased. As a result, problems have been caused such that the dielectric constant of the toner is decreased, and that the charge quantity under a high-temperature high-humidity environment is extremely lowered.
Thus, when, in the wet type manufacturing methods, especially in the emulsification polymerization aggregation method, the addition amount of the magnetic powder is increased, it is required that the dispersion liquid be uniformly mixed while the magnetic powder precipitation being prevented.